Chemistry (school) · Part 05
Moles and calculations
Counting atoms by weighing them, and the chemistry sums that follow.
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- Relative atomic massThe average mass of an atom of an element compared with carbon-12 (which is 12). It is the larger number next to each symbol on the periodic table. It has no units.
- Relative formula massThe sum of the relative atomic masses of all the atoms shown in a formula. For a molecule it is also called relative molecular mass (Mr).
- MoleThe amount of a substance that contains 6.02 x 10^23 particles. One mole of a substance weighs its relative formula mass in grams.
- Avogadro constantThe number of particles in one mole of any substance. Its value is 6.02 x 10^23 per mole.
- Moles from massTo find the number of moles, divide the mass in grams by the relative formula mass. Moles = mass / Mr.
- Limiting reactantThe reactant that is used up first, which stops the reaction and limits how much product forms. The other reactant is in excess.
- Percentage yieldHow much product you really made compared with the most you could have made. Yield = actual mass / maximum mass x 100.
- ConcentrationHow much of a substance is dissolved in a given volume of solution. It is often measured in grams per dm3 or in moles per dm3.
- Molar gas volumeOne mole of any gas takes up 24 dm3 at room temperature and pressure. This lets you convert between moles of a gas and its volume.